Diego in Seattle wrote: ↑Sun Jul 09, 2023 1:56 pm
I don't know how much (if any) June gloom the inland areas get. If you get any does that alter the ability to charge?
We do get "June Gloom" but it generally clears earlier here than on the coast, where somedays it never clears up. The time of year and the weather both make a big difference, which I will try to illustrate with three charts. The month and day on these charts seem bass ackwards because they use the European convention of putting the day of the month first. These are 24 hour usage charts from: two days ago (July 7); June 13, in the height of June Gloom, and one of the shortest days of the year, in terms of daylight (December 7).
There are basically four values shown in the chart.
- The yellow is the output of the solar PV system.
- The dark blue is the total electric usage of the house (minus the electric stove and oven).
- The light blue is household use being covered by the PV system.
- The green line is the "state of charge" of the battery. Basically, all of our usage after 4:00 pm, if not provided by the PV system, comes from the battery. The battery then charges from the grid between midnight and 6:00 am.
July 6
The battery starts at 75% state of charge at midnight, and charges to 100% at 3:00 am. At 3:00 am the EV charges for three hours. I always charge the EV between 3:00 and 6:00, but I only need to do it every couple of weeks. We start getting a little solar output just after 6:00 am. At 9:00 am the blue jumps up, that's the pool pump coming on. It's pretty cloudy in the morning but the sun comes out at about 10:00 am. The solar output peaks at about 1:30 pm at 5.2 kW. We start using battery power at about 6:30 pm when the sun goes down and use about 25% of its 20 kWh storage by midnight, when it starts charging again. Those three peaks in the evening are probably the dishwasher, the heat pump water heater and the heat pump clothes dryer. Without the car charging, the total solar production is a lot more than our 24 hours consumption.
June 13
This is a similar profile to July 6, except that there's no car charging and the sun is intermittent. It never comes out permanently even in the afternoon. Battery operation is just about the same as on July 6. Even with the intermittent sun we're probably producing as much or more than we use. If there was a temporary power outage I would turn off the pool pump and save probably 25% to 30% of the daily usage. Note that up until now we have not been using AC yet this year, which would add some usage in the afternoon and evening.
December 9
In December, near the winter solstice, our peak PV output was only 3.2 kW, and the daylight hours are greatly reduced. Most of the usage is for space heat coming from the electric heat pump. We set the thermostat to 65 degrees when we go to bed around 10:00 pm. At 6:00 am it goes up to 70 deg, hence that big usage heating up the house in the morning. With a lot of heating going on between about 5:00 pm 10:00 pm we used about 70% of the battery storage.
If we had a power outage on December 9, we wouldn't be able to cover all of our usage with solar and the battery backup. But if I turned off the pool pump and turned the thermostat way down (it doesn't get all that cold here), I think we would be OK. Remember, we are backing up all of the house, except for the electric stove and oven. Not just the refrigerator and a few lights.
